If you are level 70, each +hit increases your dps by .08%. If you are getting 300 dps, that hit’s worth about .24 dps. If you’re getting 900 dps, that hit adds approximately .72 dps. (assuming against level 73 bosses and, still, that you have shadow focus.)

If you are level 70, each +crit increases your dps by .02%. This is regardless of your hit cap or level of your opponent. If you’re getting 300 dps that’s about .06 more dps. At 900 that’s about .18. NOTE this assumes half your damage comes from Mind Blast and SW:D. SW:P and MF cannot crit. (I don’t know, yet, about VT). Adjust based on actual proportion.

REGARDLESS OF LEVEL, each +dmg increases your dps by .29 (1/3.5). No caveats.

Now if you’re lower level you need less hit rating to get a percent difference in hit prob. As a result you’re even better off to get the + hit — but only up to a point. What’s the point? Depends on what level you intend to fight. Remember that even though you hit them more often (and so do more damage), higher levels have more damage to take. I’d set a ‘reasonable’ cap of about 3 levels above, again.

The quick and dirty calculation goes as follows:

Take the proportion of damage that comes from Mind Blast and SW:D, and halve it. That gives you your crit to hit ratio – how much one crit will add in relation to one hit.

If you’re less than level 60, take your hit rating, multiply by ten, divide by your level (round, for god’s sake), and add 1. If you’re 60 or above, don’t add the 1 at the end. This will give you a quick approximate of the percentage of DPS increase the hit will add. Determine this damage and you’re ready to compare your result to +damage. You can multiply that times 3.5 and compare to +damage or you can divide +damage by 3.5 and compare it to your first number.

About…

I've experience with many priests of many races and specs on several servers. The more I play, the more I realize how much I do not yet know. This is a share of some of what I have learned.
My main these days is Zingiber on the Undermine server.